In the above mentioned machines, the cardboard boxes are very often erected in a forming station, immediately before being introduced onto a conveying line, aimed at conveying them to subsequent filling and closing stations.
In this case, the flat folded tubular blanks, which are to form the boxes, are included in a magazine, from which the blanks are taken out one by one, by suitable means, and sent to the forming station, where they are erected by known erecting means, present therein.
There are magazines, in which the flat folded tubular blanks are arranged horizontal, or vertical, or inclined, and which have, associated thereto, withdrawing means, each time constructed in accordance with magazine conformation and with the way of feeding the forming station downstream.
The flat folded tubular blanks, when supplied by the paper-transformation industry, have a good rigidity and planarity, considered positive characteristics for automated manipulation, which make the blanks easily “machinable” articles, according to the technical jargon.
On the other hand, the same blanks weigh a lot, obviously, the bigger the blank, the bigger its weight, which is to be taken in consideration especially during the magazine designing, so as to obtain an efficient support action for a stack, big enough to permit long-lasting uninterrupted operation times, without hidering withdrawal of single blanks by the means designed for it.
An interesting known technical solution has been described in the European Patent Application EP 06121373.2, filed by the same Applicant, which discloses a “Method for withdrawing flat folded piled up articles from the open bottom of a magazine and an apparatus for carrying out such method”
According to the apparatus described in the above application, the stack of flat folded tubular blanks is inclined with respect to the vertical, and the bottommost blank is supported, at the lower side, by a horizontal conveying belt, and at the opposite, higher side, by oscillating support means.
The particular set-up of the blanks brings about the advantage that only a small part of the stack weight bears on the oscillating support means.
Said oscillating support means move between a holding configuration and a release configuration, in time relation with the operation of a blade, which is inserted between the bottommost blank and the one immediately above; in this way, the bottommost blank is released while the stack above is held.
After having been released, the bottommost blank falls onto the conveyor below, due to gravity, performing an arc oscillation, which has its center in a position corresponding to the blank lower side, and then the conveyor is operated to transfer the blank, now arranged horizontal, to a box forming station downstream.
The blanks are so suitably oriented in the magazine, that said high and low sides coincide with pre-creasing lines forming hinge joints between respective adjacent face-to-face walls; this allows, firstly, supporting the stack in the blanks maximum rigidity direction and, secondly, facilitating at the same time blade insertion, due to the rounded section of the two superimposed hinge creasing lines.
The just described technical solution has shown to be efficient and reliable in most cases, except for a case in which the section of the box to be obtained, according to the erecting plate, is a square.
In this case, in flat configuration, diagonally opposite pre-creasing lines, situated in the middle of the blank, are exactly one over another, unlike in the rectangular section case, in which they are shifted.
For this reason, the blanks are less resistant to bending; therefore the ones situtate at the bottom of the stack can lose the planarity and assume a curved downward conformation, due to the weight resting on them.
The above mentioned possibility affects negatively the functionality of the oscillating support means, which can lose the engagement with the stack, or of the moving blade, which can get stuck during insertion between two blanks.
These drawbacks are amplified with the blanks increasing dimensions, and consequently weight.